Estimating a municipal water supply reliability

Figures & data

Table 1. Typical demand figure for commercial and institution establishments in urban areas

Usage	Demand allowance
Small businesses, shops and offices	Up to 35 liter/capita/day (applied as per capita allowance to the whole urban population)
Offices	65 liters/day/employee*
Departmental stores	100−135 liters/day/employee*
Hospitals	350–500 liters/day/bed
Hotels	250 liters/day/bed
Schools	25–75 liters/day/pupil*

^* Note: These figures should only be applied when the above are operating or open.

Source: Walliingford Ltd (2003).

Figure 1. Map of Nigeria showing study area and delineated river Oyun catchment.

Table 2. Salient features of Oyun reservoir and dam

Dam height	9.8 m
Location	6 km north of Offa
Catchment area (Adedayo, 2014)	830 km^2
Spillway crest elevation	406.58 m.a.s.l
Spillway length	80 m
Embankment	409.5 m.a.s.l
Gross storage volume	3500000 m^3
Net storage volume	2900000 m^3

Source: KWWC (2009).

Figure 2. Offa water demand trend between 1996 and 2008.

Figure 3. Projection of Offa population and annual domestic demand.

Table 3. Flow frequency distribution for Oyun River (Mm³)

Exceedence probability (%)	Annual flow (Mm^3)
	Normal	Log normal	Log Pearson
99	1.38	7.59	7.82
95	6.83	9.86	9.23
90	9.79	11.37	11.42
85	11.73	12.30	12.83
80	13.09	13.02	13.36
75	14.61	14.15	13.91

Walliingford, H. R. (2003). Handbook for the assessment of catchment water demand and use. Oxon: HR Walliingford.

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Adedayo, I. T. (2014). GIS application in the evaluation of peak runoff hydrograph for Oyun River watershed in Kwara state using remote sensing data ( MGIS thesis). Department of Geography and Environmental Sciences, University of Ilorin, Nigeria.

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KWWC. (2009). Kwara State Water Corporation. Ilorin, Kwara State, Nigeria.

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